An organic electroluminescence (EL) device that utilizes an organic substance is a promising inexpensive solid-state emitting large full-color display, and has been extensively developed.
The organic EL device normally includes an emitting layer and a pair of opposing electrodes disposed on either side of the emitting layer. When an electric field is applied between the electrodes, electrons and holes are injected into the emitting layer respectively from the cathode and the anode. The electrons and the holes recombine in the emitting layer to produce an excited state, and the energy is emitted as light when the excited state returns to the ground state.
It is difficult to improve the performance of an organic EL device in which the hole-injecting function, the electron-injecting function, and the emitting function are implemented by a single layer. Therefore, the performance of an organic EL device has been improved by providing a plurality of organic layers that differ in function between the electrodes. A structure in which three or more layers such as a hole-transporting layer, an emitting layer, and an electron-transporting layer are stacked between two electrodes has been generally employed.
An organic EL device that was developed in an early stage was insufficient in terms of the drive voltage, the luminous efficiency, and the durability. Therefore, various technical improvements have been made to address this problem. For example, Patent Documents 1 and 2 disclose an organic EL device material that aims at improving the drive voltage, the luminous efficiency, and the durability.
Patent Document 1 discloses a material that includes an anthracene skeleton and an imidazole skeleton as an electron-injecting/transporting material that may improve the lifetime and the efficiency of the device. Patent Document 2 discloses a nitrogen-containing heterocyclic derivative that includes a specific imidazole skeleton as an electron-transporting material that may improve the luminous efficiency at a low voltage.
Specifically, Patent Documents 1 and 2 improve the performance of the organic EL device by utilizing a nitrogen-containing heterocyclic derivative as the electron-transporting material.
Patent Document 3 aims at improving the lifetime, the luminance, and the power consumption of an organic emitting device, and discloses an organic layer that includes an anthracene derivative compound and an ion metal complex, or two types of anthracene derivative compound.
Patent Document 4 discloses a compound that includes a benzofluoranthene skeleton as a dopant material for an emitting layer.